I thought I'd chime in just to share what I've seen. Back when the iPhone 4 was just being launched, it really caught on with practically all of my friends and family. So a LOT of people I know have an iPhone 4.
The 4 was silky smooth up to 4.2.1. Then came 4.3 and Apple did something with the UI that made practically every device that supported 4.3 slower, and extremely stuttery and laggy.
iOS 5 fixed the problem on most devices but the 4 definitely still stutters. If I look at the iPhone 4s of all the people I mentioned above, there is definitely stuttering and skipping when unlocking the phone, opening the multitasking tray, or opening and closing an app. Even the 3GS, while slower, is still silky smooth. I'm making a video showing the UI smoothness and speed between the devices so I'll share that when I can.
I think Intell hit the nail on the head with this one.
The 4S, meanwhile, is a world above and beyond the 3GS and 4. While many people agree that it's not worth an upgrade from the 4, the results are definitely noticeable. The 4S is as smooth as butter and extremely quick when doing everything, even if you're heavily multitasking on it.
Totally agree. Same sediments here as well! But the iPod Touch 4th generation runs iOS 5 silky smooth. As a iPod touch 4th Gen owner myself, I clearly noticed it using both devices. I just don't get it. They run the same processor, has the same display. The iPhone 4 even had a higher amount of ram than the iPod. So why is the iPhone 4 seem to be underperforming than the iPod touch 4G? I'm pinning it on software instead for now. It seems that Apple has forgotten to optimize the software correctly for the iPhone 4 or something.
The 4S is great. Yes, its worlds beyond my 4 in terms of hardware. A 1Ghz processor nowadays seem to be rubbish. I would love to get the 4S if I had a wad of money. I do have some money now and could upgrade now if I could but obviously its not practical to get the 4S when the new one is just months away.
And please do upload a video of it if you can. I'll be the first to watch.